5.0 MPI Outdrive Gear Ratio

[bigdaddypt]

I have an 86 Sea Ray Sundancer 250 project boat. I have a donor boat with a 5.0 Mercruiser MPI (260 HP) with a Gen II Outdrive with a 1:62 gear ratio. My initial thought was this was incorrect as I was under the impression that V-8's had the 1:47 ratio. I did a little research and saw that in some cases, the 5.0 MPI would be matched with the 1:62. The donor boat was a 20' Larson bowrider, much smaller and lighter than the Sea Ray.

Obviously, I want to get the gear ratio correct for my setup. My understanding after doing some research is that for some larger, heavier boats the 5.0 MPI was paired with the 1:62 ratio to get better hole shot but would result in less top-end. Just looking for some advice on if I should keep the 1:62 or try and acquire a 1:47.

Also, I don't even know where to begin with the prop for this setup, with either drive ratio.

 

[tpenfield]

IMO, keep the 1.62 and adjust as needed with the selection of prop pitch. Don't expect to win any races with a 25 foot boat and 5.0 engine combo though . . . It may be OK, but probably not great.

 

[Bondo]

Ayuh,.... I agree with Ted, the 1.65:1 is a better match, considerin' the size of the boat,.....

 

[alldodge]

4800 pound searay, 2700 pound Larson, 5.0 mpi, I'm going to say you would be better with a 2.0. your way down with the HP and torque. The 5.0 IMO isn't much better then the V6

 

[Scott Danforth]

I would be looking for a bravo drive to put behind the searay. the 1.62 is a better ratio for the larger boat. you will probably be in the 17P or 15P range with the Alpha drive. you are going to need all the hole shot help you can get.

 

[bigdaddypt]

Thanks for the replies. The boat had a 5.0 MPI 230 hp with a B III drive. Reason I went with the setup is price and that the motor has the same hp that the boat had stock with an Alpha 1 Gen 1 drive. Not trying to win any races, simply a reliable cruiser for the family.

 

[Scott Danforth]

HP isnt an issue here. getting it transmitted is. hence the reason your boat originally had a BIII. I suggest selling your Alpha and finding a BIII.

 

[thumpar]

What happened to the B3? They put those on for better handling while docking and holeshot. That is a big boat that probably never came with an Alpha in any configuration.

 

[alldodge]

It's a 1986

 

[thumpar]

It's a 1986

He posted that it had a B3 so at some point it was swapped.

 

[bigdaddypt]

Original setup was a 5.7 260 carb with alpha drive back in 86. Previous owner got it with the 5.0 mpi with B3 drive. He sold the motor/drive/gimbal separetely. I got the boat for free for a project.

 

[thumpar]

If the donor boat has everything from pulley to prop I would stick it in. The ratio is correct for a boat like that. You can always keep your eye out for a B3 at a good price for next winters project and make some of your money back selling the Alpha setup.

When it was converted to the B3 did they use a thru hull raw water pickup? Just something to keep in mind if they did.

 

[alldodge]

Original setup was a 5.7 260 carb with alpha drive back in 86. Previous owner got it with the 5.0 mpi with B3 drive. He sold the motor/drive/gimbal separetely. I got the boat for free for a project.

After you get it all done sure appreciate letting us know how it all worked out

 

[bigdaddypt]

Will definitely be creating a thread for this project and a You Tube channel. My dream is to restore a larger cruiser like this.

The previous setup.did not have a thru hull water pickup but I will be having one. The donor is a closed cooling system and I want to keep it that way as it'll be a salt water boat.

 

[alldodge]

Thanks, but if you wouldn't mind, post in this thread with a link to your new one. Old guys like me might miss the new thread

 

[bigdaddypt]

Will do. Thinking about this, ideally I would like a B3 drive on it. If I'm doing this might as well do it right even if it takes an extra year to acquire the B3 drive. They ain't cheap!

 

[alldodge]

Do enough looking around you could find one a bit cheaper, just have to look in the right place. But going the bravo route with an alpha transom assembly you will need a different transom bell housing. Might be easier to just get a Bravo transom assembly. Look on Offshore Only classifieds for all kinds or stuff, they also have a wanted section

 

[thumpar]

If you can find a cheap B1 setup you could throw that on and then later put a B3 lower on it. That way you wouldn't have to change the transom later to switch from Alpha to Bravo. Just throwing out ideas if you plan on a B3 in the end.

 

[bigdaddypt]

Thanks for the tips. Much appreciated!

 

[FreeBeeTony]

Gotta agree the 5.0 is very light in a 25' boat........